Separate merge list for subblock merge candidates and intra-inter techniques harmonization for video coding

ABSTRACT

The present disclosure relates to methods and apparatuses for encoding video data into a bitstream and for decoding video data received in a bitstream. A second control flag indicating whether or not to use multi-hypothesis prediction for intra and inter mode is generated and transmitted only conditionally, upon a determination whether or not separate merge list technique for subblock merge candidates is used. On the other hand, a decoder is capable of deciding usage of multi-hypothesis prediction for intra and inter mode and separate merge list technique for subblock merge candidates even though the second control flag is transmitted only conditionally.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/240,210, filed on Apr. 26, 2021, which is a continuation ofInternational Application No. PCT/RU2019/050201, filed on Oct. 25, 2019,which claims the Priority of U.S. provisional application No.62/751,552, filed on Oct. 27, 2018. All of the afore-mentioned patentapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present application (disclosure) generally relate tothe field of picture processing and more particularly to harmonizationof two methods with each other. More specifically, embodiments proposemethods of joint usage and signaling a separate merge list for subblockmerge candidates and multi-hypothesis prediction for intra and intermode techniques.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

SUMMARY

The present disclosure provides apparatuses and methods for encoding anddecoding video.

The present disclosure aims to harmonize usage and signaling ofmulti-hypothesis prediction for intra and inter mode together withseparate merge lists for subblock merge candidates.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further implementation forms are apparent fromthe dependent claims, the description and the figures.

According to a first aspect of the disclosure, a method of encodingvideo data into a bitstream is provided. The method comprises using afirst technique and/or a second technique. The first technique comprisesusing a separate merge list for subblock merge candidates. The secondtechnique comprises multi-hypothesis prediction for intra and intermode. The method comprises, for a coding block, transmitting a firstcontrol block in the bitstream and, depending on whether the firsttechnique is used for the coding block, transmitting or not transmittinga second flag in the bitstream. The first control flag indicates whetherto use the first technique. The second control flag indicates whether touse the second technique.

According to a second aspect of the disclosure, a method of decodingvideo data received in the bitstream is provided. The method comprisesusing a first technique and/or a second technique. The first techniquecomprises using a separate merge list for subblock merge candidates. Thesecond technique comprises multi-hypothesis prediction for intra andinter mode. The method comprises, for a coding block, receiving thefirst control flag from the bitstream, wherein the first control flagindicates whether to use the first technique, and and, depending onwhether the first technique is used for the coding block, receiving asecond control flag from the bitstream. The second control flagindicates whether to use the second technique.

It is the particular approach of the present disclosure to generate andtransmit a second control flag indicating whether or not to usemulti-hypothesis prediction for intra and inter mode only conditionally,upon a determination whether or not separate merge list technique forsubblock merge candidates is used. On the other hand, the decoder iscapable to decide about usage of multi-hypothesis prediction for intraand inter mode and separate merge list technique for subblock mergecandidates although the second control flag is transmitted onlyconditionally.

In one embodiment, the second coding flag is transmitted if and only ifthe first technique is not used for the coding block.

In one embodiment, the second control flag is transmitted if the codingblock is quoted in merge mode. In one embodiment, the second controlflag is not transmitted if the coding block is not coded in merge mode.In one embodiment, the second control flag is transmitted if the codingblock is coded in skip mode. In one embodiment, the second control flagis not transmitted if the coding block is not coded in skip mode or inmerge mode.

Hence, signaling according to the particular approach of the presentdisclosure is applicable either in merge mode, or in skip mode, or inboth merge and skip modes.

In one embodiment, only of the first technique is not used, the secondcontrol flag is received.

Hence, the decoder may directly infer from the presence of the secondcontrol flag in the received bit stream that the separate merge listtechnique is not used for a current coding block. Thus, evaluation ofthe first control flag indicating whether or not to use the separatemerge list technique for subblock candidates is only necessary if thesecond control flag is not included in the received bitstream.

In one embodiment, the second control flag is received if the codingblock is coded in merge mode. In one embodiment, the second control flagis not received if the coding block is not coded in merge mode. In oneembodiment, second control flag is received if the coding block is codedin skip mode. In one embodiment, the second control flag is not receivedif the coding block is not coded in skip mode.

The encoding and the decoding methods defined in the claims, thedescription and the figures can each be performed by an encodingapparatus and a decoding apparatus, respectively.

According to a third aspect, the disclosure relates to an encodercomprising processing circuitry for carrying out a method according tothe first aspect as such for any of its implementation forms.

According to a fourth aspect, the disclosure relates to a decodercomprising processing circuitry for carrying out a method according tothe second aspect as such any of its implementation forms.

According to a fifth aspect, the disclosure relates to an encoder. Theencoder comprises one or more processors and a non-transitorycomputer-readable storage medium coupled to the processors and storingprogramming for execution by the processors. The programming, whenexecuted by the processors, configures the decoder to carry out themethod according to the first aspect as such or any of itsimplementation forms.

According to a sixth aspect, the disclosure relates to a decoder. Thedecoder comprises one or more processors and a non-transitorycomputer-readable storage medium coupled to the processors and storingprogramming for execution by the processors. The programming, whenexecuted by the processors, configures the decoder to carry out themethod according to the second aspect as such any of its implementationforms.

According to a seventh aspect, the disclosure relates to an encoder forvideo encoding of video data into a bitstream, the encoder comprisingmeans for performing a first technique and/or a second technique. Thefirst technique comprises using a separate merge list for subblock mergecandidates. The second technique comprises multi-hypothesis predictionfor intra and inter mode. The encoder further comprises means for, for acoding block, transmitting a first control block in the bitstream andmeans for, depending on whether the first technique is used for thecoding block, transmitting or not transmitting a second flag in thebitstream, The first control flag indicates whether to use the firsttechnique. The second control flag indicates whether to use the secondtechnique.

According to an eighth aspect, the disclosure relates to a decoder forvideo decoding of video data received in a bitstream. The decodercomprises means for performing a first technique and/or a secondtechnique. The first technique comprises using a separate merge list forsubblock merge candidates. The second technique comprisesmulti-hypothesis prediction for intra and inter mode. The decoderfurther comprises means for, for a coding block, receiving the firstcontrol flag from the bitstream, wherein the first control flagindicates whether to use the first technique, and means for, dependingon whether the first technique is used for the coding block, receiving asecond control flag from the bitstream. The second control flagindicates whether to use the second technique.

According to a further aspect, the disclosure relates to anon-transitory computer-readable medium carrying a program code which,when executed by a computer device, causes the computer device toperform a method according to the first or second aspect.

Possible implementation forms of the encoder and decoder caudal theseventh and sixth aspects correspond to the possible implementationforms of the methods according to the first and second aspects.

An apparatus for encoding or for decoding a video stream may include aprocessor and a memory. The memory stores instructions that cause theprocessor to perform the encoding or decoding method.

For each of the encoding or decoding methods disclosed herein, acomputer-readable storage medium is proposed, the storage medium havingstored thereon instructions that when executed cause one or moreprocessors to encode or decode video data. The instructions cause theone or more processors to perform the respective encoding or decodingmethod.

Furthermore, for each of the encoding or decoding methods disclosedherein, a computer program product is proposed. The computer programproduct comprises program code for performing the respective method.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

In addition, the present disclosure further provides the followingembodiments.

A encoded bit stream of a video data, comprises, multiply syntaxelements which include a first control flag, and a second flag beingconditionally signaled based on the first control flag, the firstcontrol flag indicates that if a first technique is used, wherein, thefirst technique (S101) comprises using a separate merge list forsubblock merge candidates; and the second control flag indicates that ifa second technique is used, wherein, the second technique (S103)comprises multi-hypothesis prediction for intra and inter mode.

A computing storage medium, storing a bit stream decoded by a videodecoding device, the bit stream comprise a number of coding blocks of animage or video signal, and a number of syntax elements which include afirst control flag, and a second flag being conditionally signaled basedon the first control flag, the first control flag indicates that if afirst technique is used, wherein, the first technique (S101) comprisesusing a separate merge list for subblock merge candidates; and thesecond control flag indicates that if a second technique is used,wherein, the second technique (S103) comprises multi-hypothesisprediction for intra and inter mode.

A non-transitory computer-readable storage medium storing videoinformation generated by using any of the encoding method of claim 1 to6 of the pending claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the disclosure are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the disclosure;

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the disclosure;

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the disclosure;

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the disclosure;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 is a flowchart illustrating an exemplary encoding methodaccording to embodiments of the present disclosure; and

FIG. 7 is a flowchart illustrating an exemplary decoding methodaccording to embodiments of the present disclosure.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the disclosure orspecific aspects in which embodiments of the present disclosure may beused. It is understood that embodiments of the disclosure may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present disclosure isdefined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method operations are described, a correspondingdevice may include one or a plurality of units, e.g., functional units,to perform the described one or plurality of method operations (e.g.,one unit performing the one or plurality of operations, or a pluralityof units each performing one or more of the plurality of operations),even if such one or more units are not explicitly described orillustrated in the figures. On the other hand, for example, if aspecific apparatus is described based on one or a plurality of units,e.g., functional units, a corresponding method may include one operationto perform the functionality of the one or plurality of units (e.g., oneoperation performing the functionality of the one or plurality of units,or a plurality of operations each performing the functionality of one ormore of the plurality of units), even if such one or plurality ofoperations are not explicitly described or illustrated in the figures.Further, it is understood that the features of the various exemplaryembodiments and/or aspects described herein may be combined with eachother, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g., by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g., by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g., by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions(e.g., intra- and inter predictions) and/or re-constructions forprocessing, i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3 .

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g., a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g., to a destinationdevice 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e.optionally, comprise a picture source 16, a pre-processor (orpre-processing unit) 18, e.g., a picture pre-processor 18, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g., a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g., an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g., from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2 ).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g., the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g., a video decoder30), and may additionally, i.e. optionally, comprise a communicationinterface or communication unit 28, a post-processor 32 (orpost-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 isconfigured to receive the encoded picture data 21 (or any furtherprocessed version thereof), e.g., directly from the source device 12 orfrom any other source, e.g., a storage device, e.g., an encoded picturedata storage device, and provide the encoded picture data 21 to thedecoder 30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g., a direct wired or wireless connection,or via any kind of network, e.g., a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g., packets,and/or process the encoded picture data using any kind of transmissionencoding or processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g., to send andreceive messages, e.g., to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g., encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5 ).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g., the decoded picture 31, to obtain post-processedpicture data 33, e.g., a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g., colorformat conversion (e.g., from YCbCr to RGB), color correction, trimming,or re-sampling, or any other processing, e.g., for preparing the decodedpicture data 31 for display, e.g., by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g., to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g., anintegrated or external display or monitor. The displays may, e.g.,comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g., a video encoder 20) or the decoder 30 (e.g., avideo decoder 30) or both encoder 20 and decoder 30 may be implementedusing processing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented using processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.

The decoder 30 may be implemented using processing circuitry 46 toembody the various modules as discussed with respect to decoder 30 ofFIG. 3 and/or any other decoder system or subsystem described herein.The processing circuitry may be configured to perform the variousoperations as discussed later. As shown in FIG. 5 , if the techniquesare implemented partially in software, a device may store instructionsfor the software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g., notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

For convenience of description, embodiments of the disclosure aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of thedisclosure are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2 , the video encoder 20 comprisesan input 201 (or input interface 201), a residual calculation unit 204,a transform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3 ). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20. Pictures &Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g., via input 201, apicture 17 (or picture data 17), e.g., picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g., previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.,YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g., like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 color format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2 ) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g., one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g., aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g., a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, bean M×N (M-column by N-row) array of samples, or an M×N array oftransform coefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredencode the picture 17 block by block, e.g., the encoding and predictionis performed per block 203.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g., by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g., a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g., by inversetransform processing unit 212 (and the corresponding inverse transform,e.g., by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g., bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g., a typeof transform or transforms, e.g., directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g., by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209. The quantization process may reducethe bit depth associated with some or all of the transform coefficients207. For example, an n-bit transform coefficient may be rounded down toan m-bit Transform coefficient during quantization, where n is greaterthan m. The degree of quantization may be modified by adjusting aquantization parameter (QP). For example, for scalar quantization,different scaling may be applied to achieve finer or coarserquantization. Smaller quantization step sizes correspond to finerquantization, whereas larger quantization step sizes correspond tocoarser quantization. The applicable quantization step size may beindicated by a quantization parameter (QP). The quantization parametermay for example be an index to a predefined set of applicablequantization step sizes. For example, small quantization parameters maycorrespond to fine quantization (small quantization step sizes) andlarge quantization parameters may correspond to coarse quantization(large quantization step sizes) or vice versa. The quantization mayinclude division by a quantization step size and a corresponding and/orthe inverse dequantization, e.g., by inverse quantization unit 210, mayinclude multiplication by the quantization step size. Embodimentsaccording to some standards, e.g., HEVC, may be configured to use aquantization parameter to determine the quantization step size.Generally, the quantization step size may be calculated based on aquantization parameter using a fixed point approximation of an equationincluding division. Additional scaling factors may be introduced forquantization and dequantization to restore the norm of the residualblock, which might get modified because of the scaling used in the fixedpoint approximation of the equation for quantization step size andquantization parameter. In one example implementation, the scaling ofthe inverse transform and dequantization might be combined.Alternatively, customized quantization tables may be used and signaledfrom an encoder to a decoder, e.g., in a bitstream. The quantization isa lossy operation, wherein the loss increases with increasingquantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g., directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g., by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g., an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g., adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g., by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samples. Theloop filter unit is, e.g., configured to smooth pixel transitions, orotherwise improve the video quality. The loop filter unit 220 maycomprise one or more loop filters such as a de-blocking filter, asample-adaptive offset (SAO) filter or one or more other filters, e.g.,a bilateral filter, an adaptive loop filter (ALF), a sharpening, asmoothing filter or a collaborative filter, or any combination thereof.Although the loop filter unit 220 is shown in FIG. 2 as being an in loopfilter, in other configurations, the loop filter unit 220 may beimplemented as a post loop filter. The filtered block 221 may also bereferred to as filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as sampleadaptive offset information), e.g., directly or encoded via the entropyencoding unit 270, so that, e.g., a decoder 30 may receive and apply thesame loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g., previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g., previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g., if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g., an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g., filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g., fromdecoded picture buffer 230 or other buffers (e.g., line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g., inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g., an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g., from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitionthe block 203 into smaller block partitions or sub-blocks (which formagain blocks), e.g., iteratively using quad-tree-partitioning (QT),binary partitioning (BT) or triple-tree-partitioning (TT) or anycombination thereof, and to perform, e.g., the prediction for each ofthe block partitions or sub-blocks, wherein the mode selection comprisesthe selection of the tree-structure of the partitioned block 203 and theprediction modes are applied to each of the block partitions orsub-blocks.

In the following the partitioning (e.g., by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203into smaller partitions, e.g., smaller blocks of square or rectangularsize. These smaller blocks (which may also be referred to as sub-blocks)may be further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g., at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g., partitioned into two or moreblocks of a next lower tree-level, e.g., nodes at tree-level 1(hierarchy-level 1, depth 1), wherein these blocks may be againpartitioned into two or more blocks of a next lower level, e.g.,tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioningis terminated, e.g., because a termination criterion is fulfilled, e.g.,a maximum tree depth or minimum block size is reached. Blocks which arenot further partitioned are also referred to as leaf-blocks or leafnodes of the tree. A tree using partitioning into two partitions isreferred to as binary-tree (BT), a tree using partitioning into threepartitions is referred to as ternary-tree (TT), and a tree usingpartitioning into four partitions is referred to as quad-tree (QT).

As mentioned before, the term “block” as used herein may be a portion,in particular a square or rectangular portion, of a picture. Withreference, for example, to HEVC and VVC, the block may be or correspondto a coding tree unit (CTU), a coding unit (CU), prediction unit (PU),and transform unit (TU) and/or to the corresponding blocks, e.g., acoding tree block (CTB), a coding block (CB), a transform block (TB) orprediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto the PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quadtree structure similar tothe coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), Quad-tree and binary tree (QTBT) partitioning is used topartition a coding block. In the QTBT block structure, a CU can haveeither a square or rectangular shape. For example, a coding tree unit(CTU) is first partitioned by a quadtree structure. The quadtree leafnodes are further partitioned by a binary tree or ternary (or triple)tree structure. The partitioning tree leaf nodes are called coding units(CUs), and that segmentation is used for prediction and transformprocessing without any further partitioning. This means that the CU, PUand TU have the same block size in the QTBT coding block structure. Inparallel, multiple partition, for example, triple tree partition wasalso proposed to be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of(pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g., non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g., as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g., non-directionalmodes like DC (or mean) mode and planar mode, or directional modes,e.g., as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g., stored in DBP 230) and other inter-prediction parameters, e.g.,whether the whole reference picture or only a part, e.g., a searchwindow area around the area of the current block, of the referencepicture is used for searching for a best matching reference block,and/or e.g., whether pixel interpolation is applied, e.g., half/semi-peland/or quarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct modemay be applied.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2 ). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g., reconstructed blocks of one or a pluralityof other/different previously decoded pictures 231, for motionestimation. E.g., a video sequence may comprise the current picture andthe previously decoded pictures 231, or in other words, the currentpicture and the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g., receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

Motion compensation unit may also generate syntax elements associatedwith the blocks and the video slice for use by video decoder 30 indecoding the picture blocks of the video slice.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g., a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g., in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g., encodedbitstream 21), e.g., encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g., data that represents pictureblocks of an encoded video slice and associated syntax elements.

In the example of FIG. 3 , the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g., a summer 314), aloop filter 320, a decoded picture buffer (DBP) 330, an inter predictionunit 344 and an intra prediction unit 354. Inter prediction unit 344 maybe or include a motion compensation unit. Video decoder 30 may, in someexamples, perform a decoding pass generally reciprocal to the encodingpass described with respect to video encoder 100 from FIG. 2 .

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214 the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3 ), e.g., any or all of inter prediction parameters (e.g.,reference picture index and motion vector), intra prediction parameter(e.g., intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 maybe configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode selection unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g., by parsing and/or decoding, e.g., by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice to determine a degree of quantization and,likewise, a degree of inverse quantization that should be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 313 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g., by parsing and/or decoding, e.g., by entropy decoding unit 304)to determine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g., adder or summer 314) may beconfigured to add the reconstructed residual block 313, to theprediction block 365 to obtain a reconstructed block 315 in the sampledomain, e.g., by adding the sample values of the reconstructed residualblock 313 and the sample values of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g., to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g., a bilateral filter, anadaptive loop filter (ALF), a sharpening, a smoothing filters or acollaborative filters, or any combination thereof. Although the loopfilter unit 320 is shown in FIG. 3 as being an in loop filter, in otherconfigurations, the loop filter unit 320 may be implemented as a postloop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g.,via output 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g., by parsingand/or decoding, e.g., by entropy decoding unit 304). Mode selectionunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode selection unit 360 is configured to generateprediction block 365 for a picture block of the current video slicebased on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344(e.g., motion compensation unit) of mode selection unit 360 isconfigured to produce prediction blocks 365 for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 304. For inter prediction,the prediction blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference frame lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in DPB 330.

Mode selection unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors and other syntax elements, and uses the predictioninformation to produce the prediction blocks for the current video blockbeing decoded. For example, the mode selection unit 360 uses some of thereceived syntax elements to determine a prediction mode (e.g., intra orinter prediction) used to code the video blocks of the video slice, aninter prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter encoded video block of theslice, inter prediction status for each inter coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current operation may be further processed andthen output to the next operation. For example, after interpolationfiltering, motion vector derivation or loop filtering, a furtheroperation, such as Clip or shift, may be performed on the processingresult of the interpolation filtering, motion vector derivation or loopfiltering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limited to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP (advanced temporal motion vector prediction) modes,temporal motion vectors, and so on). For example, the value of motionvector is constrained to a predefined range according to itsrepresenting bit. If the representing bit of motion vector is bitDepth,then the range is −2{circumflex over ( )}(bitDepth−1)˜2{circumflex over( )}(bitDepth−1)−1, where “{circumflex over ( )}” means exponentiation.For example, if bitDepth is set equal to 16, the range is −32768˜32767;if bitDepth is set equal to 18, the range is −131072˜131071. Hereprovides two methods for constraining the motion vector.

Method 1: remove the overflow MSB (most significant bit) by followingoperationsux=(mvx+2^(bitDepth))%2^(bitDepth)  (1)mvx=(ux>=2^(bitDepth−1))?(ux−2^(bitDepth)):ux  (2)uy=(mvy+2^(bitDepth))%2^(bitDepth)  (3)mvy=(uy>=2^(bitDepth−1))?(uy−2^(bitDepth)):uy  (4)

For example, if the value of mvx is −32769, after applying formula (1)and (2), the resulting value is 32767. In computer system, negativedecimal numbers are stored as two's complement. The two's complement of−32769 is 1,0111,1111,1111,1111 (17 bits), then the MSB is discarded, sothe resulting two's complement is 0111,1111,1111,1111 (decimal number is32767), which is same as the output by applying formula (1) and (2).ux=(mvpx+mvdx+2^(bitDepth))%2^(bitDepth)  (5)mvx=(ux>=2^(bitDepth−1))?(ux−2^(bitDepth)):ux  (6)uy=(mvpy+mvdy+2^(bitDepth))%2^(bitDepth)  (7)mvy=(uy>=2^(bitDepth−1))?(uy−2^(bitDepth)):uy  (8)

The operations may be applied during the sum of mvp (motion vectorpredictor) and mvd (motion vector difference), as shown in formula (5)to (8).

Method 2: remove the overflow MSB by clipping the valuevx=Clip3(−2^(bitDepth−1),2^(bitDepth−1)−1,vx)vy=Clip3(−2^(bitDepth−1),2^(bitDepth−1)−1,vy)

where the definition of function Clip3 is as follow:

${{Clip}3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{x;} & {z < x} \\{y;} & {z > y} \\{z;} & {otherwise}\end{matrix} \right.$

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations can be practiced with a single processor as shown, e.g.,the processor 502, advantages in speed and efficiency can be achievedusing more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

In recent development of video coding, more sophisticated techniques andschemes for prediction have emerged.

One such technique is multi-hypothesis prediction. Initially, the term“multi-hypothesis prediction” was introduced to extend motioncompensation with one prediction signal to the linear superposition ofseveral motion-compensated prediction signals. More recently, thisapproach has been generalized to combining an existing prediction modewith an extra merge indexed prediction. This includes, in particular,multi-hypothesis prediction for intra and inter mode (or, in otherwords, combining intra and inter mode, cf., for instance, Joint VideoExperts Team (JVET), document JVET-L0100-v3, entitled “CE10.1.1:Multi-hypothesis prediction for improving AMVP mode, skip or merge mode,and intra mode”, 12th Meeting: Macao, CN, 3-12 Oct. 2018). This approachapplies multi-hypothesis prediction to improve intra mode, by combiningone intra prediction and one merge indexed prediction. In other words, alinear combination of both an intra and an inter prediction block isused.

Another technique is to introduce and use separate merge lists forsub-block merge candidates, i.e. separate from merge candidate lists forthe regular merge mode, on the block level (cf., for instance, JointVideo Experts Team (JVET), document JVET-L0369-v2, entitled “CE4:Separate list for sub-block merge candidates (Test 4.2.8))”, 12thMeeting: Macao, CN, 3-12 Oct. 2018). This technique is particularlyapplicable to the above mentioned ATMVP and affine modes.

Multi-hypothesis prediction for intra and inter mode usage is controlledby mh_intra_flag, which specifies whether multi-hypothesis predictionfor intra and inter mode is enabled or not for a current block. In theprior art, the flag mh_intra_flag is transmitted conditionally dependingon merge_affine_flag according to the following syntax in Table 1:

TABLE 1 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {...  } else { /* MODE_INTER */   if( cu_skip_flag[ x0 ][ y0 ] ) {    if( ...   && cbWidth >= 8 && cbHeight >= 8)      merge_affine_flag[x0 ][ y0 ] ae(v)    if( merge_affine_flag[ x0 ][ y0 ] = = 0 &&MaxNumMergeCand > 1 ) {       if( mvd_l1_zero_flag == 0 )       mh_merge_flag[ x0 ][ y0 ] ae(v)      merge_idx[ x0 ][ y0 ] ae(v)    }   } else {    merge_flag[ x0 ][ y0 ] ae(v)    if( merge_flag[ x0][ y0 ] ) {      if( sps_affine_enabled_flag && cbWidth >= 8 &&cbHeight >= 8 &&       ( MotionModelIdc[ x0 − 1 ][ y0 + cbHeight − 1 ]!= 0 | |        MotionModelIdc[ x0 − 1 ][ y0 + cbHeight ] != 0 | |       MotionModelIdc[ x0 − 1 ][ y0 − 1 ] != 0 | |       MotionModelIdc[ x0 + cbWidth − 1 ][ y0 − 1 ] != 0 | |       MotionModelIdc[ x0 + cbWidth ][ y0 − 1 ]] != 0 ) )      merge_affine_flag[ x0 ][ y0 ] ae(v)       if(   merge_affine_flag[x0 ][ y0 ] = =   0 && MaxNumMergeCand > 1 )        mh_merge_flag[ x0 ][y0 ] ae(v)       if(   merge_affine_flag[ x0 ][ y0 ] = =   0 &&       mh_merge_flag[ x0 ][ y0 ] == 0 ) mh_intra_flag[ x0 ][ y0 ] ae(v)      if( mh_intra_flag[ x0 ][ y0 ] )        mh_intra_mode_idx [ x0 ][y0 ]      if( merge_affine_flag[ x0 ][ y0 ] = =0 && MaxNumMergeCand > 1)       merge_idx[ x0 ][ y0 ] ae(v)    } else { ... }

Thus, mh_intra_flag was conditionally signaled under the condition thatmerge_affine_flag is zero. This means that joint usage of affine mergewith mh_intra_flag, i.e. multi-hypothesis prediction for intra and intermode, is disabled. However, it does allow usage of ATMVP withmh_intra_flag.

After recent adoption of separate merge list for subblock mergecandidates, affine merge candidates were coupled together with atmvpmerge candidates and usage of these subblock candidates is controlled bya newly introduced parameter called merge_subblock_flag. No separatemerge_affine_flag is used any longer. Thus the syntax does not allowdetermining a case when merge_affine mode is not used but atmvp is usedany longer. A new way of signaling multi-hypothesis prediction combiningintra and inter mode in the presence of separate merge lists forsubblock merge candidates has been developed in the framework of thepresent disclosure.

The disclosure proposes plural methods of usage and signalingmulti-hypothesis prediction for intra and inter mode assuming thepresence of separate merge lists for subblock merge candidates in thecodec. Plural ways of harmonization are possible which are included inthe current disclosure. Also usage of multi-hypothesis prediction forintra and inter mode in case of skip mode is disclosed.

According to one general aspect of the present disclosure, a method ofvideo encoding of video data into a bitstream and a method of videodecoding of video data received in a bitstream are provided.

The method of video encoding comprises applying a first technique and/ora second technique. The first technique comprises using a separate mergelist for subblock merge candidates. The second technique comprisesmulti-hypothesis prediction for intra and inter mode. The methodcomprises transmitting a first control flag in the bitstream, whereinthe first control flag indicates whether to use the first technique andtransmitting a second control flag in the bitstream, wherein the secondcontrol flag indicates whether to use the second technique.

The method of video decoding comprises applying a first technique and/ora second technique. The first technique comprises using a separate mergelist for subblock merge candidates. The second technique comprisesmulti-hypothesis prediction for intra and inter mode. The methodcomprises receiving a first control flag from the bitstream, wherein thefirst control flag indicates whether to use the first technique andreceiving a second control flag from the bitstream, wherein the secondcontrol flag indicates whether to use the second technique.

In accordance with embodiments, the usage of the technique ofmulti-hypothesis prediction for intra and inter mode is controlledindependently of usage of the separate merge list for subblock mergecandidates technique. In other words, in such embodiments, signaling ofthe first control flag (merge_subblock_flag) is performed independentlyof signaling of the second control flag (mh_intra_flag).

In one embodiment multi-hypothesis prediction for intra and inter modeis controlled by mh_intra_flag which is signaled without dependency ofmerge_subblock_flag. In this case multi-hypothesis prediction for intraand inter mode is possible for both subblock modes: affine and atmvp aswell as for normal merge. Syntax in Table 2 below demonstrate possibleways of signaling mh_intra_flag in an embodiment.

TABLE 2 Descriptor .coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {...  } else { /* MODE_INTER */   if( cu_skip_flag[ x0 ][ y0 ] ) {    if(...   && cbWidth >= 8   &&   cbHeight >= 8)     merge_subblock_flag[ x0][ y0 ] ae(v)    if( merge_subblock_flag[ x0 ][ y0 ]   = = 0   &&  MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)    if(  merge_subblock_flag[ x0 ][ y0 ] = =   1 && MaxNumSubblockMergeCand > 1)    merge_subblock_idx[ x0 ][ y0 ] ae(v)   } else {    merge_flag[ x0 ][y0 ] ae(v)    if( merge_flag[ x0 ][ y0 ] ) {     if( ...   && cbWidth >=8   &&   cbHeight >= 8)      merge_subblock_flag[ x0 ][ y0 ] ae(v)    if(   merge_subblock_flag[ x0 ][ y0 ] = =   0 && MaxNumMergeCand > 1)      merge_idx[ x0 ][ y0 ] ae(v)     if(   merge_subblock_flag[ x0 ][y0 ] = =   1 && MaxNumSubblockMergeCand > 1 )      merge_subblock_idx[x0 ][ y0 ] ae(v)      mh_intra_flag[ x0 ][ y0 ] ae(v)    } else { ... }

In the Table 2 above, use of multi-hypothesis prediction combining intraand intra mode is restricted to coding blocks in the merge mode.

TABLE 3 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {...  } else { /* MODE_INTER */   if( cu_skip_flag[ x0 ][ y0 ] ) {    if(...   &&   cbWidth >= 8   &&   cbHeight >= 8)     merge_subblock_flag[x0 ][ y0 ] ae(v)    if( merge_subblock_flag[ x0 ][ y0 ]   = = 0   &&  MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)    if(  merge_subblock_flag[ x0 ][ y0 ] = =   1 && MaxNumSubblockMergeCand > 1)    merge_subblock_idx[ x0 ][ y0 ] ae(v)    mh_intra_flag[ x0 ][ y0 ]ae(v)   } else {    merge_flag[ x0 ][ y0 ] ae(v)    if( merge_flag[ x0][ y0 ] ) {     if( ...   && cbWidth >= 8   &&   cbHeight >= 8)     merge_subblock_flag[ x0 ][ y0 ] ae(v)     if(  merge_subblock_flag[ x0 ][ y0 ] = =   0 && MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)     if(   merge_subblock_flag[ x0 ][ y0] = =   1 && MaxNumSubblockMergeCand > 1 )      merge_subblock_idx[ x0][ y0 ] ae(v)      mh_intra_flag[ x0 ][ y0 ] ae(v)    } else { ... }

In the preceding Table 3, use of multi-hypothesis prediction combiningintra and intra mode can be applied to both coding blocks in the mergemode and coding blocks in the skip mode.

In an embodiment of the present disclosure, multi-hypothesis predictionfor intra and inter mode is controlled by mh_intra_flag which issignaled based on merge_subblock_flag. In this case multi-hypothesisprediction for intra and inter mode is possible only if both subblockmodes: affine and atmvp are disabled. In other words, multi-hypothesisprediction for intra and inter modes is possible in normal merge modebut a combination of multi-hypothesis prediction for intra and intermode with separate merge lists for subblock merge candidates isdisabled. Syntax Table 4 below demonstrate possible ways of signalingmh_intra_flag in this embodiment.

TABLE 4 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {...  } else { /* MODE_INTER */   if( cu_skip_flag[ x0 ][ y0 ] ) {    if(...   &&   cbWidth >= 8   &&   cbHeight >= 8)     merge_subblock_flag[x0 ][ y0 ] ae(v)    if( merge_subblock_flag[ x0 ][ y0 ]   = = 0   &&  MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)    if(  merge_subblock_flag[ x0 ][ y0 ] = =   1 && MaxNumSubblockMergeCand > 1)    merge_subblock_idx[ x0 ][ y0 ] ae(v)   } else {    merge_flag[ x0 ][y0 ] ae(v)    if( merge_flag[ x0 ][ y0 ] ) {     if( ...   &&  cbWidth >= 8   &&   cbHeight >= 8)      merge_subblock_flag[ x0 ][ y0 ]ae(v)     if(   merge_subblock_flag[ x0 ][ y0 ] = =   0 &&MaxNumMergeCand > 1 )      merge_idx[ x0 ][ y0 ] ae(v)     if(  merge_subblock_flag[ x0 ][ y0 ] = =   1 && MaxNumSubblockMergeCand > 1 )     merge_subblock_idx[ x0 ][ y0 ] ae(v)      if( merge_subblock_flag[x0 ][ y0 ] = = 0 )       mh_intra_flag[ x0 ][ y0 ] ae(v)     } else {... }

In the Table 4 above, use of multi-hypothesis prediction combining intraand intra mode is restricted to coding blocks in the merge mode.

TABLE 5 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {...  } else { /* MODE_INTER */   if( cu_skip_flag[ x0 ][ y0 ] ) {    if(...   &&   cbWidth >= 8   &&   cbHeight >= 8)     merge_subblock_flag[x0 ][ y0 ] ae(v)    if( merge_subblock_flag[ x0 ][ y0 ]   = = 0   &&  MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)    if(  merge_subblock_flag[ x0 ][ y0 ] = =   1 && MaxNumSubblockMergeCand > 1)    merge_subblock_idx[ x0 ][ y0 ] ae(v)     if( merge_subblock_flag[ x0][ y0 ] = = 0 )      mh_intra _flag[ x0 ][ y0 ] ae(v)   } else {   merge_flag[ x0 ][ y0 ] ae(v)    if( merge_flag[ x0 ][ y0 ] ) {    if( ...   &&   cbWidth > = 8   &&   cbHeight >= 8)     merge_subblock_flag[ x0 ][ y0 ] ae(v)     if(  merge_subblock_flag[ x0 ][ y0 ] = =   0 && MaxNumMergeCand > 1 )     merge_idx[ x0 ][ y0 ] ae(v)     if(   merge_subblock_flag[ x0 ][ y0] = =   1 && MaxNumSubblockMergeCand > 1 )      merge_subblock_idx[ x0][ y0 ] ae(v)      if( merge_subblock_flag[ x0 ][ y0 ] = = 0 )      mh_intra_flag[ x0 ][ y0 ] ae(v)    } else { ... }

In the preceding Table 5, use of multi-hypothesis prediction combiningintra and intra mode can be applied to both coding blocks in the mergemode and coding blocks in the skip mode.

In the framework of the above embodiment, the encoder signals themh_intra_flag (“second flag”, also called clip_flag) only if separatemerge lists for subblock candidates are disabled, i.e. ifmerge_subblock_flag (“first flag”) is zero. On the other hand, a decoderreceiving a bitstream in which mh_intra_flag is included determines bydefault that separate merge lists for subblock candidates are disabled.

In the following, the processing in accordance with embodimentsdescribed above will be explained with reference to the flowcharts ofFIGS. 6 and 7 .

FIG. 6 is a flowchart illustrating an encoder side process according toan embodiment of the present disclosure.

The process starts with a decision whether or not to use a separatemerge list for subblock candidates, in operation S101. If this is notthe case (S101: No), processing proceeds to operation S103. In operationS103, it is decided, whether or not multi-hypothesis predictioncombining intra and inter mode is used. Independently of the outcome ofthe decision, processing subsequently proceeds to operation S105. Inoperation S105, an mh_intra_flag is generated as a parameter to besignaled in the bitstream. More specifically, if multi-hypothesisprediction for intra and inter mode is used (S103: Yes), a value “1” isset to the mh_intra_flag and if multi-hypothesis prediction for intraand inter flag is not used (S103: No), a value “0” is set to themh_intra_flag (not shown in the drawing).

Subsequently, processing proceeds to operation S107. In the case when itis decided in operation S101 to use a separate merge list for subblockcandidates (S101: Yes), processing proceeds directly from operation S101to operation S107.

In operation S107, a merge_subblock_flag is generated as a parameter tobe signaled in the bitstream. More specifically, in case of usage of aseparate merge list, i.e. when the flow proceeds from S101: Yes, a value“1” is set to the merge_subblock_flaf and in case when the flow comesfrom S101: No through S103 and S105, i.e. when no separate merge list isused, the merge_subblock_flag is set to a value “0” (not shown in thedrawing).

Hence, multi-hypothesis prediction for intra and inter mode is used onlyconditionally upon the condition that separate merge lists for subblockcandidates are not used. Therefore, the merge_subblock_flag is alwaysgenerated but an mh_intra_flag is generated only if no separate mergelist for intra and inter mode is used. Subsequently, a bitstreamincluding the merge_subblock_flag and conditionally (if themerge_subbock_flag is 0) also including the mh_intra_flag is generatedin operation S109 and the processing ends.

FIG. 7 is a flowchart illustrating a decoder side processing accordingto an embodiment of the present disclosure.

The processing starts with operation S201, in which a received bitstreamis parsed. In subsequent operation S203, it is checked, whether or notthere is an mh_intra_flag in the bitstream. If this is the case (S203:Yes), processing proceeds to operation S207. In operation S207, themh_intra_flag is evaluated in order to decide whether multi-hypothesisprediction for intra and inter mode is to be used in the decoding,depending on the value of the parsed mh_intra_flag. In case themh_intra_flag has the value of 1, decoding is performed with usingmulti-hypothesis prediction for intra and inter mode in operation (S207:Yes->S211), and the processing ends. Otherwise, i.e. when themh_intra_flag has a value of 0 (S207: No), multi-hypothesis predictionis not used (and neither is a separate merge list for subblockcandidates).

If, on the other hand, it is determined in operation S203 that there isno mh_intra_flag (S203: No), processing proceeds to operation S204. Inoperation S204, a subblock_merge_flag received from the bitstream isevaluated in order to determine in the following operation (S205)whether or not to use a separate merge list for subblock candidates.

In operation S205, if the subblock_merge_flag has a value of 1, it isdetermined that the separate merge list is to be used (S205: Yes), andthe processing proceeds to operation S209, in which decoding isperformed using the separate merge list. Otherwise, i.e. when thesubblock_merge_flag has a value of 0 (S205: No), it is determined thatdecoding is performed without_using the separate merge list (and withoutthe multi-hypothesis prediction for intra and inter mode), and theprocessing flow ends.

Hence, according to the embodiment, from the existence of themh_intra_flag in the parsed bitstream (S203: Yes) it is directlyinferred that separate merge lists for subblock candidates are not used.

In other words, the merge_subblock_flag, which is always included in thebitstream and received, is analyzed only in the case when nomh_intra_flag is included in the bitstream. Thus; in any case, only asingle flag needs to be evaluated on the decoder side.

More generally speaking, according to the present disclosure, usage ofthe technique of multi-hypothesis prediction for intra and inter mode iscontrolled based on usage of the separate merge list for subblock mergecandidates technique. More specifically, in accordance with theembodiment of FIG. 7 , the technique of multi-hypothesis prediction forintra and inter mode can be used if and only if separate merge list forsubblock merge candidates technique is disabled.

The above mentioned embodiments allow to harmonize multi-hypothesisprediction for intra and inter mode with separate merge list forsubblock merge candidates. Embodiments which also enable usage ofmulti-hypothesis prediction for intra and inter mode in block skip modeadditionally allow to achieve coding gain in respect to basic design.Embodiments which include conditional signaling of mh_intra_flag basedon usage of separate merge lists for subblock merge candidates have theadditional benefit of reducing signaling overhead, because themh_intra_flag does not need to be signaled in each case.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   ÷ Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

-   -   Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

-   -   The summation of f(i) with i taking all integer values from x up        to and including y.    -   x % y Modulus. Remainder of x divided by y, defined only for        integers x and y with x>=0 and y>0.        Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of        y; otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   ∧ Bit-wise “exclusive or”. When operating on integer arguments,        operates on a two's complement representation of the integer        value. When operating on a binary argument that contains fewer        bits than another argument, the shorter argument is extended by        adding more significant bits equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0. Assignment operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   += Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −= Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}{x;} & {x>=0} \\{{- x};} & {x < 0}\end{matrix} \right.$

-   -   A sin(x) the trigonometric inverse sine function, operating on        an argument x that is in the range of −1.0 to 1.0, inclusive,        with an output value in the range of −π÷2 to π÷2, inclusive, in        units of radians    -   A tan(x) the trigonometric inverse tangent function, operating        on an argument x, with an output value in the range of −π÷2 to        π÷2, inclusive, in units of radians

${{A\tan}2\left( {y,x} \right)} = \left\{ \begin{matrix}{{{A\tan}\left( \frac{y}{x} \right)};} & {x > 0} \\{{{{A\tan}\left( \frac{y}{x} \right)} + \pi};} & {{x < 0}{\&\&}{y>=0}} \\{{{{A\tan}\left( \frac{y}{x} \right)} - \pi};} & {{x < 0}\&\&{y < 0}} \\{{+ \frac{\pi}{2}};} & {{x==0}\&\&{y>=0}} \\{{- \frac{\pi}{2}};} & {otherwise}\end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

${{{Clip}1_{Y}(x)} = {{Clip}3\left( {0,{\left( {1{\operatorname{<<}{BitDepth}_{Y}}} \right) - 1},x} \right)}}{{{Clip1}_{C}(x)} = {{Clip}3\left( {0,{\left( {1{\operatorname{<<}{BitDepth}_{C}}} \right) - 1},x} \right)}}{{{Clip}3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{x;} & {z < x} \\{y;} & {z > y} \\{z;} & {otherwise}\end{matrix} \right.}$

-   -   Cos(x) the trigonometric cosine function operating on an        argument x in units of radians.    -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{{c + d};} & {{b - a}>={d/2}} \\{{c - d};} & {{a - b} > {d/2}} \\{c;} & {otherwise}\end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e        is the natural logarithm base constant 2.718 281 828 . . . ).    -   Log 2(x) the base-2 logarithm of x.    -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ {{\begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix}{{Round}(x)}} = {{{{Sign}(x)}*{{Floor}\left( {{{Abs}(x)} + 0.5} \right)}{{Sign}(x)}} = \left\{ \begin{matrix}{1;} & {x > 0} \\{0;} & {x==0} \\{{- 1};} & {x < 0}\end{matrix} \right.}} \right.} \right.$

-   -   Sin(x) the trigonometric sine function operating on an argument        x in units of radians    -   Sqrt(x)=√{square root over (x)}    -   Swap(x,y)=(y,x)    -   Tan(x) the trigonometric tangent function operating on an        argument x in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.        The table below specifies the precedence of operations from        highest to lowest; a higher position in the table indicates a        higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE 6 Operation precedence from highest (at top of table) to lowest(at bottom of table) operations (with operands x, y, and z) ″x++, ″x −−″ ″!x″, ″−x″(as a unary prefix operator) x^(y)${{\,^{''}x}*y^{''}},{{\,^{''}x}/y^{''}},{{\,^{''}x} \div y^{''}},{\,^{''}\frac{x}{y}^{''}},{{\,^{''}x}\% y^{''}}$″x + y″, ″x − y″ (as a two-argument operator),$\,^{''}{\sum\limits_{i = x}^{y}{f(i)}^{''}}$ ″x << y″, ″x >> y″ ″x <y″, ″x <= y″, ″x > y″, ″x >= y″ ″x = = y″, ″x != y″ ″x & y″ ″x | y″ ″x && y″ ″x || y″ ″x ? y : z″ ″x . . . y″ ″x = y″, ″x += y″, ″x −= y″

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

if(condition 0)

-   -   statement 0 else if(condition 1)    -   statement 1

. . .

else /* informative remark on remaining condition */

-   -   statement n        may be described in the following manner:

. . . as follows / . . . the following applies:

-   -   If condition 0, statement 0    -   Otherwise, if condition 1, statement 1    -   . . .    -   Otherwise (informative remark on remaining condition), statement        n.

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in thetext is introduced with “ . . . as follows” or “ . . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . ” statements can be identified by matching “ . . . asfollows” or “ . . . the following applies” with the ending “Otherwise, .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

if(condition 0a && condition 0b)

-   -   statement 0

else if(condition 1a∥condition 1b)

-   -   statement 1

. . .

else

-   -   statement n        may be described in the following manner:

. . . as follows / . . . the following applies:

-   -   If all of the following conditions are true, statement 0:        -   condition 0a        -   condition 0b    -   Otherwise, if one or more of the following conditions are true,        statement 1:        -   condition 1a        -   condition 1b    -   . . .    -   Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

if(condition 0)

-   -   statement 0

if(condition 1)

-   -   statement 1        may be described in the following manner:

When condition 0, statement 0

When condition 1, statement 1

Embodiments, e.g., of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g., with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

What is claimed is:
 1. A method, comprising: for a coding block,transmitting a value of a first control flag in a bitstream, wherein thevalue of the first control flag equals to 1 indicates a first techniqueis to be used, wherein the first technique comprises using a separatemerge list for subblock merge candidates; and in response to determiningthe first technique is not used for the coding block, transmitting avalue of a second control flag in the bitstream, wherein the value ofthe second control flag equals to 1 indicates a second technique is tobe used, wherein the second technique comprises multi-hypothesisprediction for intra and inter mode, wherein the value of the secondcontrol flag is transmitted if and only if the first technique is notused for the coding block.
 2. The method according to claim 1, furthercomprising: if the coding block is coded in merge mode, transmitting thesecond control flag.
 3. The method according to claim 2, furthercomprising: if the coding block is not coded in merge mode, determiningthat the second control flag is not to be transmitted.
 4. The methodaccording to claim 1, further comprising: if the coding block is codedin skip mode, transmitting the second control flag.
 5. The methodaccording to claim 4, further comprising: if the coding block is notcoded in skip mode or in merge mode, determining that the second controlflag is not to be transmitted.
 6. A method comprising: for a codingblock, receiving a value of a first control flag from a bitstream,wherein the value of the first control flag equals to 1 indicates afirst technique is to be used, wherein the first technique comprisesusing a separate merge list for subblock merge candidates; and inresponse to determining that the value of the first control flag isequal to 0, receiving a value of a second control flag from thebitstream, wherein the value of the second control flag equals to 1indicates a second technique is to be used, wherein the second techniquecomprises multi-hypothesis prediction for intra and inter mode, whereinthe value of the second control flag is transmitted if and only if thefirst control flag is equal to
 0. 7. The method according to claim 6,further comprising: if the coding block is coded in merge mode,receiving the second control flag.
 8. The method according to claim 7,further comprising: if the coding block is not coded in merge mode,determining that the second control flag is not to be received.
 9. Themethod according to claim 6, further comprising: if the coding block iscoded in skip mode, receiving the second control flag.
 10. The methodaccording to claim 9, further comprising: if the coding block is notcoded in skip mode or in merge mode, determining that the second controlflag is not to be received.
 11. A decoder comprising: at least oneprocessor; and one or more memories coupled to the at least oneprocessor and storing programming instructions for execution by the atleast one processor to cause the decoder to: for a coding block, receivea value of a first control flag from a bitstream, wherein the value ofthe first control flag equals to 1 indicates a first technique is to beused, wherein the first technique comprises using a separate merge listfor subblock merge candidates; and in response to determining that thevalue of the first control flag is equal to 0, receive a value of asecond control flag from the bitstream, wherein the value of the secondcontrol flag equals to 1 indicates a second technique is to be used,wherein the second technique comprises multi-hypothesis prediction forintra and inter mode, wherein the value of the second control flag istransmitted if and only if the first control flag is equal to
 0. 12. Thedecoder according to claim 11, wherein the programming instructions forexecution by the at least one processor to cause the decoder further to:if the coding block is coded in merge mode, receive the second controlflag.
 13. The decoder according to claim 12, wherein the programminginstructions for execution by the at least one processor to cause thedecoder further to: if the coding block is not coded in merge mode,determine that the second control flag is not to be received.
 14. Thedecoder according to claim 11, wherein the programming instructions forexecution by the at least one processor to cause the decoder further to:if the coding block is coded in skip mode, receive the second controlflag.
 15. The decoder according to claim 14, wherein the programminginstructions for execution by the at least one processor to cause thedecoder further to: if the coding block is not coded in skip mode or inmerge mode, determine that the second control flag is not to bereceived.
 16. A non-transitory storage medium storing an encodedbitstream for video signals, the encoded bitstream comprises a pluralityof syntax elements, wherein the plurality of syntax elements comprises avalue of a first control flag, wherein the value of the first controlflag equals to 1 indicates a first technique is to be used, wherein thefirst technique comprises using a separate merge list for subblock mergecandidates; and when the value of the first control flag is equal to 0,the plurality of syntax elements further comprises a value of a secondcontrol flag, wherein the value of the second control flag equals to 1indicates a second technique is to be used, wherein the second techniquecomprises multi-hypothesis prediction for intra and inter mode, whereinthe value of the second control flag is comprised in the plurality ofsyntax elements if and only if the first control flag is equal to 0.